Tracked vehicle with apparatus for determining track force applied to wheels

ABSTRACT

The tracked vehicle includes a plurality of wheels and a track extending around the wheels. A force sensor is provided for generating a signal indicative of the track force applied to at least one wheel. The track force on a wheel is the force applied to the wheel by the vehicle track due to tensile forces in the track. The force applied on a wheel resulting from the interaction of the wheel with the ground over which the vehicle passes is determined by a force sensor which generates a signal indicative of the force transmitted from the wheel to the vehicle body, a linear variable induction transducer which generates signals indicative of the track force applied to the wheel, and a processor for combining the signals generated by the force sensor and linear variable induction transducer to remove from the signals those signals attributable to the track force applied to the wheel indicative of the force transmitted from the wheel to the vehicle body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to apparatus for determining the loadapplied to a wheel of a tracked vehicle by the track adjacent to thewheel.

2. Description of Related Art

It has previously been proposed to use so called "active" suspensionsystems to control the suspension of a tracked vehicle. "Active"suspension systems are suspension systems in which the wheels of thevehicle are connected to hydraulic actuators which can be controlled tocause motion of the wheels. The hydraulic actuators are controlled bycontrol processors in response to various measured physical parameters.An example of such an "active" suspension system can be seen in EuropeanPatent Publication No. 0114757.

The application of active suspension to a tracked vehicle providesproblems since in most active suspension systems it is necessary tomeasure the load transmitted by an actuator to the vehicle body. In atracked vehicle, the load transmitted by an actuator to the trackedvehicle body comprises not only the load on the wheel transmitted fromthe road, but also comprises load on the wheel due to tension in thevehicle track associated with the wheel. For correct operation of thevehicle suspension system the force on the wheel due to the track of atracked vehicle must be isolated, to allow the active suspension systemto react only to loads on the wheel due to road inputs, that is to sayloads on the wheel due to the interaction of the vehicle with theterrain over which it passes.

SUMMARY OF THE INVENTION

According to the present invention there is provided a tracked vehiclehaving a plurality of wheels and a track extending around the wheelswherein there is provided apparatus for determining the track forceapplied to at least one wheel.

The term "track force" which is used in this specification describes theforce applied to a wheel of a tracked vehicle resulting from tensileforces in the track extending around the wheels of the vehicle.

According to the present invention there is also provided a trackedvehicle having a plurality of wheels and a track extending around thewheels wherein there is provided means for determining the force appliedon to a wheel resulting from the interaction of the wheel with theground over which the vehicle passes comprising:

a first signal generating means which generates signals indicative ofthe force transmitted from the wheel to the vehicle body,

second signal generating means which generates signals indicative of thetrack force applied to the wheel and

processor means for combining the signals generated by the first andsecond signal generating means to remove from the signals indicative ofthe force transmitted from the wheel to the vehicle body those signalsattributable to the track force applied to the wheel.

Preferably the apparatus for determining the track force applied to atleast one wheel includes means for determining tensile forces in thetrack.

Preferably the means for determining tensile forces includes sensormeans for generating signals indicative of the position of one or moremovable wheels of the vehicle.

Preferably the means for determining tensile forces in the trackcalculates the tensile forces as a function of the position of thewheels and the length of the track.

In a first preferred embodiment the tracked vehicle has an upperplurality of wheels and a lower plurality of wheels, which lowerplurality of wheels are adjacent the ground over which the vehiclepasses, and a track extending around both the upper wheels and the lowerwheels wherein the means for determining tensile forces comprisesprocessor means for summing the distances between;

the foremost and hindmost upper wheels,

the foremost and hindmost lower wheels,

the foremost upper and the foremost lower wheels, and

the hindmost upper and the hindmost lower wheels.

In the first preferred embodiment the processor means preferablycalculates the tensile forces as the product of the summed distances anda predefined proportionality constant.

In the first preferred embodiment the upper wheels are preferablyrotatably mounted to the vehicle for rotation about axes fixed relativeto the vehicle and the lower wheels are mounted to the vehicle bysuspension means.

Also in the first preferred embodiment at least the foremost andhindmost of the lower wheels are preferably mounted to the vehicle bysuspension means which includes:

an actuator,

a force sensor to sense the force transmitted to the vehicle by theactuator and to generate signals indicative thereof and

a suspension control processor to control the actuator, wherein

the signals generated by the force sensor are modified by the processormeans to remove therefrom signals attributable to the portion of thesensed force resulting from the track force applied to the wheels asdetermined by the means for determining the track force applied to thewheels.

Preferably the suspension means further includes resilient mountingswhich deflect upon application of force to the mounted wheels and applyopposing forces proportional to the deflection of the wheels, and theprocessor means is adapted to determine the magnitude of the opposingforces and to modify the signals generated by the force sensorsassociated with the wheels to remove therefrom or add thereto signalscorresponding to the opposing forces.

Preferably the suspension control processor comprises the processormeans.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the tracked vehicle illustrating the apparatusfor determining track force applied to wheels of the tracked vehicle.

The present invention will now be described with reference to theaccompanying drawing which shows a schematic representation of thewheels and track of a tracked vehicle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the figure there can be seen a vehicle track 10 whichextends over and around two fixed wheels C and D and around five movablewheels A, B, E, F and G.

In the present embodiment described the wheels C and D are fixed and thewheels E, F and G are connected to the vehicle body by the normalpassive elements of tracked vehicles, that is to say torsion bars. Thetorsion bars are reactive components, that is to say they allow thedeflection of the wheels E, F and G in response to loads applied to E, Fand G and the deflection is proportional to load applied.

Wheels C and D are uppermost and serve to keep the track 10 in tension.One of the wheels C or D may be driven to drive the track.

The wheels A, E, F and G shall be called the "road wheels" since theyare the wheels that are closest to the surface over which the vehicletravels. Obviously, the wheels themselves do not come into contact withthe surface, but forces are transmitted from the road surface to thewheels via the portion of the vehicle track 10 engaging the wheels.

The foremost and hindmost of the road wheels, A and B, are controlled bya so-called "active" suspension system. Active suspension systems forvehicles are well known. An example of an active suspension system isfound in European patent publication no. 0114757.

Wheel A is rotatably mounted to an L-shaped arm 11. The arm 11 ismounted to the body of the tracked vehicle by a torsion bar 12. Asmentioned above, the torsion bar 12 is a passive element which applies aforce on the wheel A proportional to displacment of wheel A, from a meanposition.

The end 13 of the L-shaped arm 11 is connected to a hydraulic actuator14. The hydraulic actuator 14 in the drawings is shown as an "unequal"area actuator. The hydraulic actuator 14 comprises a piston 15 operablewithin a cylinder 16. The piston 15 defines two chambers 17 and 18within the cylinder. The piston 15 is connected to the L-shaped member13 by a connecting rod 19. The connecting rod 19 reduces the area of thepiston 15 that acts in the chamber 17, as compared with the area of thepiston 15 that acts in the chamber 18. The chamber 17 is permanentlyconnected via line 20 to a source of pressurised fluid 21. The chamber18 is connected by a line 22 to a servo-valve 23. The servo-valve 23 canconnect the chamber 18 either to a source of pressurised fluid 21 or toan exhaust for pressurised fluid 24.

If the chamber 18 is connected by the servo-valve 23 to a source ofpressurised fluid 21, then a force is applied across the piston 15 dueto the difference in the area of the two sides of the pistons acting inthe chambers 17 and 18, which force acts to rotate the L-shaped arm 11anti-clockwise and force the wheel A downwards.

If the chamber 18 is connected to the exhaust for pressurised fluid 24by the servo-valve 23 then a resultant force on the piston 15 resultswhich acts to rotate the L-shaped member 11 clockwise, forcing the wheelA upwardly.

The servo-valve 23 meters the flow of fluid into and out of the chamber18, to control the velocity of the piston 15 within the chamber 16. Bycontrolling the velocity of the piston, 15, the actuator can control thevelocity of wheel A.

The servo-valve 23 is an electrically controlled servo-valve. Theservo-valve 23 is controlled by a suspension control processor 33 whichgenerates electrical control signals and sends the control signals tothe servo-valve 23 by the line 25. The operation of the suspensioncontrol processor 33 will not be described since it has been clearlydescribed in numerous previous patent specifications for activesuspension systems for wheeled vehicles and the specific operation ofthe suspension control processor 33 is not an essential feature of thepresent invention.

A force transducer 26 is interposed between the actuator 14 and thepoint of mounting 27 of the actuator to the vehicle body. The mountingpoint 27 allows rotation of the actuator 14. The force transducer 26generates an electrical signal indicative of the force transmitted bythe actuator 14 to the vehicle body.

An L.V.I.T. (linear variable induction transducer) 29 measures thedisplacement of the piston 15 with respect to the cylinder 16. TheL.V.I.T. 29 generates signals indicative of the position of the piston15 and sends these via line 34 to the suspension control processor 33and by the lines 34 and 35 to a further processor 30, which will bedescribed hereinafter.

The wheel B is mounted in an identical fashion to the vehicle body andsimilar components have been referenced accordingly, although the forcetransducer for wheel B has been referenced 36, the actuator referenced32 and the L.V.I.T. 37, for ease of reference.

If the arrangement shown in FIG. 1 is used without modification of thesignal generated by the force transducer 26 then the suspension controlprocessor 33 will not function properly, since it will receive a signalfrom the force transducer 26 which has a component that is due to theforce exerted on the wheel A by the track 10 of the vehicle. Theprocessor will consider this force to be a "road input" to the vehicleand will control the actuator 14 accordingly. Therefore it is importantthat the signal used by the force transducer 26 is suitably modified, toprovide the control processor with a signal which is indicative solelyof the force due to the interaction of the track beneath the wheel Awith the ground.

The force signals generated by the two force transducers 26 are modifiedby processors 30 and 31 which each comprise means for determining thetrack force applied to a wheel.

Considering wheel A and its associated actuator, the processor 30receives both a signal from a force transducer 26 indicative of theforce transmitted by the actuator 14 to the vehicle body and also aposition signal generated by the L.V.I.T. 29, indicative of the positionof the piston 15 within the cylinder 16. Since the piston 15 isconnected to the L-shaped member 11, displacement of the piston 15 isproportional to the displacement of the wheel A.

Assuming the force measured by the load cell 26 to be F_(A), then theforce F_(A) is made up of three components as follows;

    FA=FR+Ft+Ftb

where

FA=force measured by load cell

Fr=force measured due to road input to wheel A

Ft=force measured due to "track force" on wheel A

Ftb=force measured due to stiffness of torsion bars

The processor 30 must act to isolate the term F_(r) which is the forcesignal that it transmits to the processor 33. The signal F_(r) is asignal indicative of force on the wheel A due to interaction of thetracked vehicle with the land over which it passes. The processor 33controls the extension of the actuator 14 in response to the forcesignal F_(r) in a known manner. Since the processor 30 must outputF_(r), the processor 30 has signal processing means which carries outthe following operation:

    Fr=FA-Ft-Ftb

However, before the operation can be conducted the processor 30 mustdetermine Ft and Ftb. Therefore the processor 30 has a means fordetermining the tensile forces in the track and means for determiningthe opposing force applied to the wheels by the torsion bars.

The method of calculation of Ftb shall now be described. The processor30 receives a signal X_(A) from the L.V.I.T. 29, indicative of thedisplacement of the piston 15 within the cylinder 16. The displacementX_(A) is functionally proportional to the rotational deflection in thetorsion bar. The relationship will depend upon the geometriccharacteristic of this suspension arrangement and can be easilycalculated from trigonometry. Similarly the force exerted on theactuator due to the torsional stiffness of the torsion bar can becalculated in trigonometry. Therefore we have the expression;

    Ftb=f.sub.1 (X.sub.A)

where

Ftb=force measured by load cell due to stiffness of torsion bar

X_(A) =measured displacement of piston in actuator controlling roadwheel A

f₂ (X)=function of measured displacement (determined by trigonometry andfrom the torsional stiffness of the torsion bar)

Turning now to the calculation of F_(t), it has been found by theapplicant that the force exerted on the wheels by the track is afunction of the sum of the following distances; between wheel A and C,between wheel C and D, between wheel D and B and between wheel B and A.This sum shall be termed the "track perimeter".

Since C and D are rotatably fixed to the chassis their axes of rotationare fixed with respect to the vehicle body. Therefore to calculate thetrack perimeter it is only necessary to consider the three distancesbetween A and C, A and B and B and D.

As mentioned above L.V.I.T.s measure the displacement of the pistons 15in the actuators 14 and 32 controlling the motion of wheels A and B. Thepistons 15 are directly connected to rigid L-shape links upon which thevehicle wheels are mounted for rotation and which are connected to thevehicle body by torsion bars. Therefore, it is possible to determinefrom the displacement of the pistons within the actuators controllingwheels A and D the displacement of wheels A and B. Therefore it ispossible to calculate the track perimeter.

The applicant has found that while there is some slackness in the track10, the force applied to the wheels by the track is approximatelydirectly proportional to the sum of distances mentioned above. However,when all slackness is taken out of the track then the force applied tothe wheels by the track is very large, since further extension of thetrack is not possible without actually extending the metal or othermaterial forming the track. Therefore in the preferred embodiment theprocessor 24 is adapted such that limits are imposed upon the extensionsof the actuators 14 and 32 controlling the road wheels A and B.

From test data the proportionality of the track tension to thecalculated track perimeter can be determined. Therefore F_(t) can becalculated as follows;

    Ft=K.sub.1 (DcD+F.sub.2 (X.sub.A)+F.sub.3 (X.sub.B)+Ft(X.sub.A, X.sub.B))

where

K₁ =constant of proportionality of "track perimeter" to Ft

DcD=distance between the fixed wheels C and D

F₂ (X_(A))=function of X_(A) giving distance between wheels A and C

F₃ (X_(B))=function of X_(B) giving distance between wheels D and B

F₄ (X_(A),X_(B))=function of X_(A) and X_(B) giving distance betweenwheels A and B

The processor 30 receives signals indicative of the measureddisplacements X_(A) and X_(B) of the wheels A and B from the L.V.I.T.'s29 and 37. Thus the processor can calculate Ft.

Having determined Ft and Ftb and knowing the measured force FA, theprocessor 30 can output a signal Fr corresponding to the suspensioncontrol processor 33.

In a similar fashion, processor 31 receives signals indicative of FB(the force measured by load cell 36), XA and XB and then calculates Ftband Ft for wheel B. The processor 31 then outputs FR for wheel B to thesuspension control processor 33.

While in the preferred embodiment the three wheels E,F and G areconnected to the vehicle body by passive elements, it should beappreciated that the wheels E,F and G can be connected to the vehiclebody by actuators and controlled by the active suspension systemcontroller 33.

While above the two wheels A and B are controlled by "unequal" areaactuators, any form of hydraulic actuator can be used. Furthermore,suitable electric actuators could be used as an alternative.

While the system described above has separate processors 35 and 31 forthe two wheels A and B, the functions of both could be performed by asingle processor. Indeed it is envisaged that the functions of the twoprocessors 30 and 31 could be performed by the central processor 31which also controls the actuators.

While the two wheels C and D are fixed in the preferred embodiment,motion of one of the wheels C or D could be controlled by an actuator tocontrol the tension within the track, as described in U.S. patentapplication Ser. No. 07/910,258 now abandoned.

From the foregoing it will be appreciated that the inventon provides asolution to the problem of controlling the suspension of trackedvehicles using standard active suspension technology.

I claim:
 1. A tracked vehicle having a plurality of wheels and a trackextending around the wheels wherein there is provided means fordetermining the force applied on to a wheel resulting from theinteraction of the wheel with the ground over which the vehicle passescomprising;a first signal generating means which generates signalsindicative of the force transmitted from the wheel to the vehicle body,second signal generating means which generates signals indicative of thetrack force applied to the wheel and processor means for combining thesignals generated by the first and second signal generating means toremove from the signals indicative of the force transmitted from thewheel to the vehicle body those signals attributable to the track forceapplied to the wheel.
 2. A tracked vehicle as claimed in claim 1 whereinthe signal means for generating signals indicative of the track forceapplied to at least one wheel includes means for determinging tensileforces in the track.
 3. A tracked vehicle as claimed in claim 2 whereinthe means for determining tensile forces includes sensor means forgenerating signals indicative of the position of one or more movablewheels of the vehicle.
 4. A tracked vehicle as claimed in claim 3wherein the means for determining tensile forces in the track calculatesthe tensile forces as a function of the position of the wheels and thelength of the track.
 5. A tracked vehicle as claimed in claim 4 havingan upper plurality of wheels and a lower plurality of wheels, whichlower plurality of wheels are adjacent the ground over which the vehiclepasses, and a track extending around both the upper wheels and the lowerwheels wherein the means for determining tensile forces comprisesprocessor means for summing the distances between;the foremost andhindmost upper wheels, the foremost and hindmost lower wheels, theforemost upper and the foremost lower wheels, and the hindmost upper andthe hindmost lower wheels.
 6. A tracked vehicle as claimed in claim 5wherein the processor means calculates the tensile forces as the productof the summed distances and a predefined proportionality constant.
 7. Atracked vehicle as claimed in claim 5 wherein the upper plurality ofwheels are rotatably mounted to the vehicle for rotation about axesfixed relative to the vehicle and the lower plurality of wheels aremounted to the vehicle by suspension means.
 8. A tracked vehicle asclaimed in claim 4 wherein at least the foremost and hindmost of thelower wheels are mounted to the vehicle by suspension means whichincludes;an actuator, a force sensor to sense the force transmitted tothe vehicle by the actuator and to generate signals indicative thereofand a suspension control processor to control the actuator, wherein thesignals generated by the force sensor are modified by the processormeans to remove therefrom signals attributable to the portion of thesensed force resulting from the track force applied to the wheels asdetermined by the means for determining the track force applied to thewheels.
 9. A tracked vehicle as claimed in claim 8 wherein thesuspension means further includes resilient mountings which deflect uponapplication of force to the mounted wheels and apply opposing forcesproportional to the deflection of the wheels and wherein the processormeans is adapted to determine the magnitude of the opposing forces andto modify the signals generated by the force sensors associated with thewheels to remove therefrom or add thereto signals corresponding to theopposing forces.
 10. A tracked vehicle as claimed in claim 8 wherein thesuspension control processor comprises therein the processor means.